The present invention relates to a method of controlling the supply and allocation of hydrogen gas in a hydrogen system of a refinery integrated with olefins and aromatics plants to convert crude oil into petrochemicals. More in detail the present invention relates to a process for converting hydrocarbons into olefins and BTXE, the converting process comprising the integration of hydrogen consuming process units with hydrogen producing process units.
US Patent application No 2012/024752 relates to a multi-stage integrated process for the production of high octane naphtha from a hydrocarbonaceous feedstock, comprising isolating a hydrocracked naphtha from a hydrocracking reaction zone effluent, providing at least a portion of the hydrocracked naphtha to a reforming reaction zone containing a reforming catalyst, contacting the at least a portion of the hydrocracked naphtha with the reforming catalyst at reforming reaction conditions and producing a hydrogen-rich stream and a reformed naphtha, and d. passing the hydrogen-rich stream to the hydrocracking reaction zone. This reference does not refer to specific olefins generating plants. The hydrocracking reaction conditions are established to achieve a target conversion of greater than 30% of the hydrocarbonaceous feedstock within the hydrocracking reaction zone, wherein the value of 30% is based on conversion of the hydrocarbonaceous feedstock to naphtha.
U.S. Pat. No. 3,972,804 relates to a method for controlling the hydrogen/hydrocarbon mole ratio and the control system in processes for the catalytic conversion of hydrocarbons in a hydrogen-containing atmosphere, in which processes the consumption of hydrogen occurs, namely hydrogen control system of a single hydrogen consuming unit. In all these processes, as in most hydrogen-producing processes such as catalytic reforming, a commonly-practiced technique involves the utilization of a hydrogen-rich vaporous phase recycled to combine with the fresh hydrocarbon charge to the reaction zone. According to this reference a charge stock composition or a product composition characteristic is sensed and the hydrogen concentration within the vaporous phase introduced into the reaction zone with the feed stock is sensed. Appropriate representative output signals are transmitted to a comparator/computer which in turn generates computer output signals which are transmitted as required to adjust reaction zone severity (temperature and pressure), charge stock flow and recycle gas flow in order to regulate the hydrogen/hydrocarbon mole ratio while simultaneously achieving the desired product quality and/or quantity. With respect to hydrogen-consuming processes comparator output signals are transmitted to regulate the quantity of make-up hydrogen introduced into the process from an external source and the flow of any required reaction zone temperature quench stream. In a hydrogen-consuming process, such as hydrocracking, that portion of the separated reaction zone effluent, containing hydrogen is insufficient, and must be supplemented by make-up hydrogen from a suitable source external of the process—i.e., catalytic reforming which produces an abundance of hydrogen.
The article “Modelling and optimisation for design of hydrogen networks for multi-period operation”, Ahmad M. I. et al, Journal of cleaner production, Elsevier, NL, vol. 18, no. 9, 1 Jun. 2010 (2010-06-01), pages 889-899 relates to a design of flexible hydrogen networks that can remain optimally operable under multiple periods of operation, also identified as flexibility. This reference only refers to refinery operations. The proposed methodology for multi-period design of hydrogen networks can take into account pressure differences, maximum capacity of existing equipment, and optimal placement of new equipment such as compressors. A hydrogen network may be described as a system of refinery processes that interact with each other through distribution of hydrogen. These refinery processes may be classified into two categories, i.e. hydrogen producers and hydrogen consumers, based on their contribution to the hydrogen network. Hydrogen producers are units that supply hydrogen to the hydrogen distribution system, such as the hydrogen plant and catalytic reforming unit. The catalytic reforming process produces hydrogen as a by-product of cyclisation and dehydrogenation reactions of hydrocarbon molecules to increase the aromatic content and the octane number of naphtha products. Hydrogen consumers are conversion processes, such as the hydrocracking process for upgrading heavy hydrocarbon fractions, hydrotreating processes to satisfy cleaner fuel specifications, lubricant plants, the isomerization process and the hydrodealkylation units. These processes employ hydrogen as a reactant to upgrade the quality of refinery products. Amongst all the hydrogen consuming processes hydrocracking and hydrotreating processes are the major hydrogen consumers.
US patent application No. 2006/287561 relates to a process for increasing the production of C2-C4 light olefin hydrocarbons by integrating a process for producing an aromatic hydrocarbon mixture and liquefied petroleum gas (LPG) from a hydrocarbon mixture and a process for producing a hydrocarbon feedstock which is capable of being used as a feedstock in the former process.
U.S. Pat. No. 4,137,147 relates to a process for manufacturing ethylene and propylene from a charge having a distillation point lower than about 360 DEG C. and containing at least normal and iso-paraffins having at least 4 carbon atoms per molecule, wherein: the charge is subjected to a hydrogenolysis reaction in a hydrogenolysis zone, in the presence of a catalyst, (b) the effluents from the hydrogenolysis reaction are fed to a separation zone from which are discharged (i) from the top, methane and possibly hydrogen, (ii) a fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule, and (iii) from the bottom, a fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, (c) only the fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule is fed to a steam-cracking zone, in the presence of steam, to transform at least a portion of the hydrocarbons with 2 and 3 carbon atoms per molecule to monoolefinic hydrocarbons; the fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, obtained from the bottom of the separation zone, is supplied to a second hydrogenolysis zone where it is treated in the presence of a catalyst, the effluent from the second hydrogenolysis zone is supplied to a separation zone to discharge, on the one hand, hydrocarbons with at least 4 carbon atoms per molecule which are recycled at least partly to the second hydrogenolysis zone, and, on the other hand, a fraction consisting essentially of a mixture of hydrogen, methane and saturated hydrocarbons with 2 and 3 carbon atoms per molecule; a hydrogen stream and a methane stream are separated from the mixture and there is fed to the steam-cracking zone the hydrocarbons of the mixture with 2 and 3 carbon atoms, together with the fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule as recovered from the separation zone following the first hydrogenolysis zone. At the outlet of the steam-cracking zone are thus obtained, in addition to a stream of methane and hydrogen and a stream of paraffinic hydrocarbons with 2 and 3 carbon atoms per molecule, olefins with 2 and 3 carbon atoms per molecule and products with at least 4 carbon atoms per molecule.
US Patent application No 2005/101814 relates to a process for improving the paraffin content of a feedstock to a steam cracking unit, comprising: passing a feedstream comprising C5 through C9 hydrocarbons including C5 through C9 normal paraffins into a ring opening reactor, the ring opening reactor comprising a catalyst operated at conditions to convert aromatic hydrocarbons to naphthenes and a catalyst operated at conditions to convert naphthenes to paraffins, and producing a second feedstream; and passing at least a portion of the second feedstream to a steam cracking unit. The ring opening reactor includes hydrogenation for converting aromatic compounds to naphthenes. Hydrogen is supplied to the ring opening reactor for the hydrogenation wherein one source of hydrogen available to use in the ring opening reactor is from the steam cracking unit generating hydrogen as a byproduct of the cracking process. The ring opening process stream can be passed to the steam cracking unit for conversion of the paraffins to ethylene and propylene, and the steam cracking unit, in addition to generating light olefins, generates a by-product known as pyrolysis gasoline (py-gas), wherein the py-gas leaving the steam cracking unit is passed to the ring opening reactor for increasing the light olefin production from a naphtha feedstream.
Conventionally, crude oil is processed, via distillation, into a number of cuts such as naphtha, gas oils and residua. Each of these cuts has a number of potential uses such as for producing transportation fuels such as gasoline, diesel and kerosene or as feeds to some petrochemicals and other processing units.
Light crude oil cuts such as naphtha and some gas oils can be used for producing light olefins and single ring aromatic compounds via processes such as steam cracking in which the hydrocarbon feed stream is evaporated and diluted with steam and then exposed to a very high temperature (750° C. to 900° C.) in short residence time (<1 second) furnace (reactor) tubes. In such a process the hydrocarbon molecules in the feed are transformed into (on average) shorter molecules and molecules with lower hydrogen to carbon ratios (such as olefins and aromatics) when compared to the feed molecules. This process also generates hydrogen as a useful by-product and significant quantities of lower value co-products such as methane and C9+ Aromatics and condensed aromatic species (containing two or more aromatic rings which share edges).
Typically, the heavier (or higher boiling point) aromatic species, such as residua are further processed in a crude oil refinery to maximize the yields of lighter (distillable) products from the crude oil. This processing can be carried out by processes such as hydro-cracking (whereby the hydro-cracker feed is exposed to a suitable catalyst under conditions which result in some fraction of the feed molecules being broken into shorter hydrocarbon molecules with the simultaneous addition of hydrogen). Heavy refinery stream hydrocracking is typically carried out at high pressures and temperatures and thus has a high capital cost.
An aspect of such a combination of crude oil distillation and steam cracking of the lighter distillation cuts is the capital and other costs associated with the fractional distillation of crude oil. Heavier crude oil cuts (i.e. those boiling beyond ˜350° C.) are relatively rich in substituted aromatic species and especially substituted condensed aromatic species (containing two or more aromatic rings which share edges) and under steam cracking conditions these materials yield substantial quantities of heavy by products such as C9+ aromatics and condensed aromatics. Hence, a consequence of the conventional combination of crude oil distillation and steam cracking is that a substantial fraction of the crude oil is not processed via the steam cracker as the cracking yield of valuable products from heavier cuts is not considered to be sufficiently high, compared to the alternative refinery fuel value.
Another aspect of the technology discussed above is that even when only light crude oil cuts (such as naphtha) are processed via steam cracking a significant fraction of the feed stream is converted into low value heavy by-products such as C9+ aromatics and condensed aromatics. With typical naphthas and gas oils these heavy by-products might constitute 2 to 25% of the total product yield (Table VI, Page 295, Pyrolysis: Theory and Industrial Practice by Lyle F. Albright et al, Academic Press, 1983). Whilst this represents a significant financial downgrade of expensive naphtha and/or gas oil in lower value material on the scale of a conventional steam cracker the yield of these heavy by-products does not typically justify the capital investment required to up-grade these materials (e.g. by hydrocracking) into streams that might produce significant quantities of higher value chemicals. This is partly because hydrocracking plants have high capital costs and, as with most petrochemicals processes, the capital cost of these units typically scales with throughput raised to the power of 0.6 or 0.7. Consequently, the capital costs of a small scale hydro-cracking unit are normally considered to be too high to justify such an investment to process steam cracker heavy by-products.
Another aspect of the conventional hydrocracking of heavy refinery streams such as residua is that these are typically carried out under compromise conditions chosen to achieve the desired overall conversion. As the feed streams contain a mixture of species with a range of ease of cracking this result in some fraction of the distillable products formed by hydrocracking of relatively easily hydrocracked species being further converted under the conditions necessary to hydrocrack species more difficult to hydrocrack. This increases the hydrogen consumption and heat management difficulties associated with the process. This also increases the yield of light molecules such as methane at the expense of more valuable species.
Refineries process crude oils into fuels such as gasoline, kerosene, diesel and fuel oils. The crude is distilled into fractions as naphtha, middle distillates, gasoils and residues. Some or all of the heavier fraction of the crude oils (gasoils and residua), may be upgraded to less heavy fractions by means of processes like fluid catalytic cracking, hydrocracking, and delayed coking.
The overall hydrogen gas mass balance in a refinery is critical for the product slate composition that can be achieved. Some refinery processes consume hydrogen gas (hydrodesulphurization, hydro-dearomatization and hydrocracking).
The hydrogen consumption is closely linked to the quality and composition of the feed: feeds with a high contaminant content, such as those with a higher concentration of unsaturated composites (for example, fractions from thermal processes, which have a significant level of olefinic compounds) lead to greater hydrogen consumption.
Some refinery units also generate hydrogen gas (e.g. catalytic reforming). In general refineries are short in hydrogen gas. The required deficit of hydrogen gas may be obtained by means of processes like steam reforming, partial oxidation of methane or gasification of the residue, or obtained from a hydrogen gas grid.
Steam cracking is a petrochemical process in which saturated hydrocarbons are broken down into smaller, often unsaturated, hydrocarbons. It is the principal industrial method for producing the lighter alkenes (or commonly olefins), including ethylene and propylene, and light aromatics. Steam cracker units are facilities in which a feedstock such as naphtha, liquefied petroleum gas (LPG), ethane, propane or butane is thermally cracked through the use of steam in a bank of pyrolysis furnaces to produce lighter hydrocarbons like olefins and light aromatics. Steam cracking also produces hydrogen gas and methane. A steam cracker consumes a small amount of its own hydrogen for hydrogenation and recycling of heavier olefins. The excess hydrogen is mainly downgraded to fuel or exported.
Propane dehydrogenation converts propane into propylene and by-product hydrogen. The propylene from propane yield is about 85-90 wt. %. Reaction by-products (mainly hydrogen) are usually used as fuel for the propane dehydrogenation reaction. As a result, propylene tends to be the only product, unless local demand exists for hydrogen. Feed hydrocracking cracking/gasoline hydrocracking (FHC/GHC) are processes which hydrocrack naphtha fractions or gasoline fractions into methane, LPG and light aromatics. Aromatic ring opening processes are able to saturate and hydrocrack multi-aromatic compounds and hydrodealkylate the remaining mono aromatic compounds.
In recent decades environmental policies and the new organization of the fuel and light-distillates market have led to significant growth in the demand for hydrogen and the introduction of considerable modifications to the production and technology aspects of refineries. Some factors increasing the demand for hydrogen are for example: the need to process increasingly heavy feeds, with a consequent increase in the level of sulphur conversion and removal, the greater restrictions imposed by environmental regulations on the sulphur content in gasolines and diesel, the increasing market reduction in the demand for high sulphur content fuel, which has made it necessary to convert the residues, which are no longer used as fuel oils, into lighter products.